I used to talk a crazy ton on the issue of players KOSing like mad crazy. You know, considering I ran essentially the only non-KOS survival group. I can’t find any of my posts, but they all boiled down to the one simple idea of the Prisoner’s Dilemma and how seemingly no matter what players will always be inclined to do what they obviously think will get them the best as an individual rather than a group. If you upsize / scale this up, groups do what is best in their own interests rather than cooperating with one another - even though cooperation would mean more spoils.
You can learn about Prisoner’s Dilemma here, and a more advanced thought of the dilemma here
I’ve completely forgot my solutions to the problem, but, most of the ideas throughout your post seem OK. Though I hate videos like the Dayz friendly Experiment. It’s a experiment without a constant variable, and has very little data (trials) done. If that makes sense.
The whole “communication is key” part is the main separation amongst players. For my group, despite being friendly individuals, we immediately KOS non-english players. Obviously we can’t be friendly to people that we can’t properly communicate with. This is an unavoidable barrier to communication in literally any game, and a game mechanic tweak will never fix this. Though ignoring different languages then yes, communication is effective.
Everyone has noticed this trend in Unturned. When you start off as a naked looting a town other people within the town usually are also naked, and never bother you. Sometimes they do out of plain boredom, but for me we simply wave and loot separately. However, in late game when people are fully decked out players will always KOS - seemingly in fear of loosing their loot. Of course it may be just for fun, but everyone loves loot, and nobody likes to loose it.
The solution could be to make looted players feel more comfortable when confronting other groups of players or even lower looted players. A ton of my group members hate trying to be friendly because they go about it wrong - they give low looted players the chance and means to kill them, such as getting close and friendly to a noob with a masterkey.
Players don’t want to take the time and effort of “being friendly” the correct way - being far away, talking out loud over a mic, and making sure they’re safe. Players can almost 100% guarantee their protection by simply keeping their stealth and avoiding you, or using their stealth to the advantage of killing you. Giving up the stealth to try and be friendly to you in a game where people can find one-shot guns in civilian towns sounds like a bad alternative.
Another problem is a lot of players may not see the incentive to be friendly. So what? I’m being friendly, giving this noob free loot, and in return he runs off? To me I see being friendly as just my personality. I love being helpful, conversating on forums, contributing to the game and groups. I like to recruit players and make them my friend. I’ve met nearly 90% of my good online friends from being friendly to them. But for the average player being friendly probably isn’t a solution or even a choice due to external factors, like not having a microphone, etc.